"The truth of the matter is that you can hardly set Christianity and Zen side by side and compare them. This would be like trying to compare mathematics and tennis. And if you are writing a book on tennis which might conceivably be read by many mathematicians, there is little point in bringing mathematics into the discussion—best to stick to the tennis."
-- Thomas Merton, Zen and the Birds of Appetite
In this typically humorous observation from Zen and the Birds of Appetite  Thomas Merton (1915-68) points out the difficulty of making tidy comparisons between Christianity and Zen Buddhism. Merton, the Trappist priest whose writings on spirituality and modern civilization made him a hero of post-World War II Catholic culture, was also a serious student of Zen Buddhism.
Merton's essays were instrumental in raising American awareness of Buddhism during the fabled "Zen boom" of the 1950s and 1960s. His lifelong affinity for Asian religions drew him deeply into a variety of eastern faith traditions, and he probably came as close as a Catholic priest can come to embracing the "way of Zen." Yet for all his success in making Zen accessible to modern Christians, Merton also perpetuated a number of assumptions that reinforce the stereotypes that have long hindered the "east-west" dialogue. Among these were his ready acceptance of the idea—which echoed the truisms of his friend and Zen mentor D.T. Suzuki (1870-1966)—that Zen was simply beyond the comprehension of the "western mind." Even though Zen had been introduced to America in 1893, and by the mid-twentieth century was well on its way to becoming a household word, it still preserved an aura of exotic "Oriental" inscrutablility.
It is probably safe to say that Zen's continuing fascination for modern people owes much to the perception that it is simply too mysterious and too paradoxical to be grasped by the common "linear-thinking" western herd. Merton's essays on Zen, while brilliant, are nevertheless permeated with the idea that Zen is, at its core, both incomparable to Christianity, and incomprehensible to the Christian.
Throughout my career as Japan scholar, I have tried to penetrate the supposed impenetrability of Zen—not to diminish the beauty of its truly mysterious paradoxes, but rather to show that there is something that can be defined, discussed, and compared with other religions. Zen is no more or less indescribable than any other form of mysticism, whether it be Christian, Islamic, Buddhist, or Jewish. I am not saying that mystical experience can be put into words, but there exists, in the historical and doctrinal landscape of Zen Buddhism, a great many recognizable features that enable the thoughtful Catholic to take bearings, and create a suitable map of the terrain–hopefully to the enrichment of his or her own faith.
What I would like to do in this essay is provide an overview of Zen, touching on its major doctrinal and practical features, in the hopes that Catholic readers will find something to appreciate, compare, and hopefully investigate further.